Stabilization of dissolved organic matter by aluminium: a toxic effect or stabilization through precipitation?

Carbon mineralization in acidic forest soils can be retarded by large concentrations of aluminium (Al). However, it is still unclear whether Al reduces C mineralization by direct toxicity to microorganisms or by decreased bioavailability of organic matter (OM) because dissolved organic matter (DOM) is precipitated by Al. We conducted an incubation experiment (6 weeks) with two DOM solutions (40 mg C litre−1) derived from two acidic forests and possessing large differences in composition. Aluminium was added to the solutions in realistic ranges for acidic soils (1.6–24 mg Al litre−1) at pHs of 3.8 and 4.5, to achieve differences in Al speciation. We determined different Al species, including the potentially toxic Al3+, by Diffusive Gradients in Thin Films (DGT) to evaluate toxic effects on microorganisms. Precipitation of OM increased with larger amounts of added Al and higher pH, and we measured a larger fraction of dissolved ‘free’ Al at pH 3.8 than at pH 4.5. Organic matter degradation decreased significantly with Al addition, and we found more organic matter degraded at pH 3.8 than at pH 4.5 for the respective Al additions. Consequently, the observed reduction in OM degradation (i.e. stabilization) cannot be explained by toxic effects of ‘free’ Al. However, C stabilization correlated significantly with C precipitation. The pH did not influence C stabilization directly, but determined the amount of C being precipitated. Phosphorus was removed along with OM by precipitation, which possibly also affected C stabilization. We conclude that C stabilization upon Al addition did not result from toxic effects, but was caused by reduced bioavailability of OM after its precipitation. The reduction in OM degradation by 65% is of great relevance for the overall C stabilization in acidic forest soils. Increasing pH and decreasing Al concentrations upon recovery from acidic deposition should therefore not result in decreased stabilization of precipitated OM.

[1]  K. Kalbitz,et al.  Contribution of dissolved organic matter to carbon storage in forest mineral soils , 2008 .

[2]  Hao Zhang,et al.  In situ measurements of metal complex exchange kinetics in freshwater. , 2007, Environmental science & technology.

[3]  J. García-Mina,et al.  Size distribution, complexing capacity, and stability of phosphate-metal-humic complexes. , 2007, Journal of agricultural and food chemistry.

[4]  Hao Zhang,et al.  Diffusion coefficients of metals and metal complexes in hydrogels used in diffusive gradients in thin films. , 2006 .

[5]  O. Borggaard,et al.  Influence of humic substances on phosphate adsorption by aluminium and iron oxides , 2005 .

[6]  Dean Hesterberg,et al.  XANES investigation of phosphate sorption in single and binary systems of iron and aluminum oxide minerals. , 2005, Environmental science & technology.

[7]  B. Glaser,et al.  Clear‐cutting of a Norway spruce stand: implications for controls on the dynamics of dissolved organic matter in the forest floor , 2004 .

[8]  P. Illmer,et al.  Effect of temperature and pH on the toxicity of aluminium towards two new, soil born species of Arthrobacter sp. , 2004, Journal of basic microbiology.

[9]  A. B. Mulder,et al.  Organic complexion of Al and Fe in acidic soil solutions comparison of diffusive gradients in thin films analyses with Models V and VI , 2003 .

[10]  B. Glaser,et al.  Changes in properties of soil-derived dissolved organic matter induced by biodegradation , 2003 .

[11]  E. Matzner,et al.  Effects of aluminium on the mineralization of dissolved organic carbon derived from forest floors , 2003 .

[12]  E. Matzner,et al.  Biodegradation of soil-derived dissolved organic matter as related to its properties , 2003 .

[13]  B. Marschner,et al.  Controls of bioavailability and biodegradability of dissolved organic matter in soils , 2003 .

[14]  J. Verstraten,et al.  Dissolved organic matter, aluminium and iron interactions: precipitation induced by metal/carbon ratio, pH and competition. , 2002, The Science of the total environment.

[15]  J. Duine,et al.  The extremely high Al resistance of Penicillium janthineleum F-13 is not caused by internal or external sequestration of Al , 2002, Biometals.

[16]  J. Verstraten,et al.  Influence of pH and metal/carbon ratios on soluble organic complexation of Fe(II), Fe(III) and Al(III) in soil solutions determined by diffusive gradients in thin films , 2002 .

[17]  Hao Zhang,et al.  Effect of solution composition, flow and deployment time on the measurement of trace metals by the diffusive gradient in thin films technique. , 2001 .

[18]  E. Matzner,et al.  Controls on the dynamics of dissolved organic carbon and nitrogen in a Central European deciduous forest , 2001 .

[19]  W. Davison,et al.  Direct in situ measurements of labile inorganic and organically bound metal species in synthetic solutions and natural waters using diffusive gradients in thin films. , 2000, Analytical chemistry.

[20]  M. Sugimoto,et al.  Isolation and characterization of acid- and Al-tolerant microorganisms. , 2000, FEMS microbiology letters.

[21]  B. Michalzik,et al.  Dynamics of dissolved organic nitrogen and carbon in a Central European Norway spruce ecosystem , 1999 .

[22]  Stefan Geyer,et al.  Spectroscopic properties of dissolved humic substances - a reflection of land use history in a fen area , 1999 .

[23]  David L. Jones.  Organic acids in the rhizosphere – a critical review , 1998, Plant and Soil.

[24]  Ken E. Giller,et al.  Toxicity of heavy metals to microorganisms and microbial processes in agricultural soils: a review , 1998 .

[25]  Zhenli He,et al.  MICROBIAL UTILIZATION AND TRANSFORMATION OF PHOSPHATE ADSORBED BY VARIABLE CHARGE MINERALS , 1998 .

[26]  R. Biesuz,et al.  Sorption of divalent metal ions on an iminodiacetic resin from artificial seawater , 1997 .

[27]  R. Martin,et al.  Interactions of Aluminum(III) with Phosphates. , 1996, Inorganic chemistry.

[28]  C. Cervantes,et al.  Microbial interactions with aluminium , 1996, Biometals.

[29]  N. Batjes,et al.  Total carbon and nitrogen in the soils of the world , 1996 .

[30]  F. Schinner,et al.  Solubilization of hardly-soluble AlPO 4 with P-solubilizing microorganisms , 1995 .

[31]  J. M. Bremner,et al.  Relationships between the denitrification capacities of soils and total, water-soluble and readily decomposable soil organic matter , 1975 .

[32]  D. F. Boltz,et al.  Spectrophotometric Determination of Phosphorus as Molybdiphosphoric Acid , 1948 .

[33]  K. Kalbitz,et al.  Precipitation of Dissolved Organic Matter by Aluminum Stabilizes Carbon in Acidic Forest Soils , 2007 .